UBC Theses and Dissertations
Cyclotron-based production of radioisotopes for medical imaging studies Hou, Xinchi
The cyclotron-based ¹⁰⁰Mo(p,2n)⁹⁹mTc reaction has been proposed as an alternative method for solving the recent shortage of ⁹⁹mTc, which is the most commonly used radioisotope in nuclear medicine. With this production method, however, even if highly enriched molybdenum is used, various radioactive and stable isotopes can be produced simultaneously with ⁹⁹mTc and they may affect the diagnostic outcome and radiation dosimetry in human studies. The objective of this thesis was to investigate the feasibility of the cyclotron-based production of ⁹⁹mTc. Towards this aim, theoretical predictions and experimental measurements were performed to investigate the quantity and purity of cyclotron-produced technetium. In this thesis, the production cross sections and yields of cyclotron-produced ⁹⁹mTc and various other radioactive and stable isotopes were calculated. Radiation doses from three radiopharmaceuticals labeled with cyclotron-produced technetium were estimated. Different conditions were considered for both yield and dosimetry calculations in order to investigate the optimal reaction parameters for producing maximum ⁹⁹mTc and minimizing other contaminants. To facilitate the complex and time-consuming calculations, a graphical user interface was developed allowing users to perform the theoretical predictions in only a few seconds. Besides theoretical estimations, quantitative experimental measurements of ⁹⁹mTc samples were performed. Gamma spectra from different cyclotron runs were analyzed. In order to investigate the image qualities for using cyclotron-produced technetium, phantom scans for both cyclotron- and reactor-produced ⁹⁹mTc at different times after end of beam were performed using SPECT. Large quantities of produced ⁹⁹mTc proved the capability of cyclotron production of ⁹⁹mTc. Both theoretical predictions and experimental analysis showed over 9 Ci of ⁹⁹mTc can be produced in a 6 hours cyclotron run when using enriched ¹⁰⁰Mo target. Besides ⁹⁹mTc, the main contributors, which influenced the production activities, patient doses and quality of images, were ⁹⁴g⁻⁹⁶gTc. These results indicated the molybdenum target used in cyclotron production should have relatively small content of ⁹⁵⁻⁹⁷Mo, which are the “reaction parents” for ⁹⁴g⁻⁹⁶gTc. Furthermore, we demonstrated that incident proton beam energies in the range of 16-19 MeV, target thicknesses degrading beam energy to 10 MeV and relatively short irradiation times (3-6 hours) corresponded to the most advantageous region for ⁹⁹mTc production.
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